With the variety of compressors available today, it can be difficult to know which you should use for your mixing sessions.
There are many different types of compressor, ranging from analog to digital and even expansion (which we we’ll cover below).
In this article we’re going to cover everything you need to know about compressor plugins, the types and which mixing situation each style is best suited for. You’ll learn about hardware compressors, vintage emulations, digital, multiband, limiters, and expanders.
Contents
VCA Compressors
VCA compressor is short for Voltage Controlled Amplifier compressor. It’s an analog compressor that uses a VCA to apply compression to an audio signal. Many VCA compressors were hardware units in the beginning, but now there are a lot of great digital re-creations of them.
VCA compressors provide a fast compression response, due to the circuitry used to control the compression. This means they’re good for controlling heavy transients, and levelling out audio.
They are the most versatile analog compressor out of the analog types, and can either sound transparent, or provide warmth and drive, depending on the settings you choose.
Like any other compressor, VCA compressors have control for Attack, Release, Threshold, Ratio, Knee and make-up gain. They additionally sometimes have support for sidechain input.
The most recognisable VCA compressor, is the SSL channel. These are analog channel strip compressors that can be bought as hardware, or as a virtual analogue plugin. Waves do a fantastic emulation of the SSL 4000E, 4000G master bus, API 2500, and many different kinds of VCA style compressors.
✅ What Are VCA Compressors Good For?
VCA Compression are popular because of its ability to sound transparent, preserve transients, and add a certain punch and thickness to sounds. It’s gives the most clean compression out of the analog types and is the most versatile analog compression too.
They are great for drum processing, and parallel compression – especially the API 2500!
Here’s a list of what VCA compressors are good for:
- Master bus compression (or 2-bus)
- Group bus compression for glue
- Preserving transients, while gluing audio
- Transient control on drums, and other sound sources
- Smoothing out recordings transparently, without adding colour
- Keeping unwanted distortion to a minimum
❌ What Are VCA Compressors Bad For?
VCA compressors do have some drawbacks. These can depend on which units you have. Most VCA’s are transparent and don’t provide much colour, drive, or warmth. Yet, you can get some that give a very distinct sound (The Focusrite Red 3 for instance).
Here’s a list of what VCA compressors are bad for:
- Adding colour
- Adding warmth
- Adding drive
FET Compressors
FET compressors use something called a “field effect transistor” to apply compression to audio. FET compressors are an analog unit that add a signature colour to sounds that isn’t heard in other types. They have a short compression response times and provide aggression, grit, warm and fuzzy compression styles.
FET compressors are one of the most common units you’ll find alongside VCA. They are an analog hardware unit, but is also used in plugin format by many modern day producers.
Some great FET plugins include the Softube FET compressor, the Waves CLA-2A (LA-2A), & CLA-76.
FET compressors were originally invented to offer a more transient friendly compression option to the Optical and Vari-mu compressors on the market at the time. They provide a very aggressive, colourful sound that’s great for a lot of things.
Add drive, warmth, and colour to your sound using FET.
Controls consist of attack, release, ratio, input, output. They don’t have threshold or knee, so are a little drawn back for control.
✅ What Are FET Compressors Good For?
FET compression provides an aggressive sound, with a very distinct colour. It’s great for adding drive and grit to sounds.
It works well as a parallel compressor, especially for drum tracks, aggressive vocals, bass and more.
Anything you want front and centre, use an FET compressor! (so poetic)
Here’s a list of what FET compressors are good for:
- Parallel compression
- Aggressive sound, warmth, drive, energy and thickness
- Compression for front and centre, in-your-face sound
- Fast, rapid compression, catching peaks
- Tracking instruments or vocals in a studio
- Limiting
❌ What Are FET Compressors Bad For?
FET compressors have some drawbacks too. They aren’t too great for transparency, and often provide a bit too much grit.
Perfect for an aggressive, fast sound but you might want to look somewhere else for smooth or natural compression.
Here’s a list of what FET compressors are bad for:
- Transparent compression
- Easy to overdo, so mostly used in parallel
- No threshold or knee control
Tube Compressors
Tube compressors are a vintage compression unit that use input voltage changes to alter the bias of the tubes – applying gain reduction to an audio signal. They provide smooth, slow, warm compression, and are good for vocals.
Although Optical compressors also use tubes in their circuitry (to apply warmth to the gain reduction), Tube compressors themselves are entirely different because they use tubes independently to control gain reduction process.
This gives an extreme warm, harmonically rich and slow compression, that is great for adding colour and fatness.
Tube compressors can also be known as Vari-mu compressors, or valve compressors.
One of the most popular Tube compressors is, the Fairchild 660, and 670. These had over 20 tubes, and 12 transformers inside, giving it an awesome, rich sound. You can get great replicas of the Fairchild today in plugin format.
The Waves collection, Puigchild 670 & 660 are a good choice.
✅ What Are Tube Compressors Good For?
Tube compressors apply a harmonically rich compression sound that is slow in response. They are especially good for vocals and masters.
It’s great for huge gain reduction without any introduced artefacts, but are generally better for small amounts of gain reduction.
Here’s a list of what Tube compressors are good for:
- Huge gain reduction without artefacts
- Master bus compression
- Parallel compression
- Harmonically rich compression
- Smooth, warm, driven compression
- Adds brightness
❌ What Are Tube Compressors Bad For?
Tube compressors also have their drawbacks. They aren’t good for transient control for instance due to their slow response.
They also lack the control other compressors have, so you might not get a transparent sound out of these.
Here’s a list of what Tube compressors are bad for:
- Lack of control
- Bad for transients due to slow response
- Not transparent
Optical Compressors
Optical compressors are a vintage unit that use light source to shine light brighter, as audio intensity increases. This light is read by an electro optical sensor, and applies gain reduction based on that. Most have a base ratio of 3:1.
Optical compressors would seem like they are fast (because of the speed of light).
But, they include a delay in compression, because it takes a while for the light to register audio intensity, and is then picked up by the sensor. This causes a slow compression response, and provides a warm sound full of character.
This makes the Optical compressor worse for transient compression, and more of an average compression used for an overall sound.
Optical compression is unique because of the response in the sensor, to the light source. It latches onto the audio signal fairly quickly, and releases fast as well, but then tapers the release off in an almost pressurised way.
They provide a smooth, musical sound and makes them popular for vocals.
Opto compressors have also become popular for Kick & Snare processing, due to the slow attack, letting the transient through. They don’t have attack, release, threshold, ratio, or knee controls and are much less versatile than the others on this list, but you’re using it for a certain crunch they provide.
The most used Opto compressors are the LA-2A and Tube-Tech CL1B. You can get both as plugins.
✅ What Are Opto Compressors Good For?
Opto compressors have a slow attack on compression, and provide a really smooth, musical sound that adds heaps of character.
Great for vocals, and good for drums. Also provide a natural squeeze to bass.
Here’s a list of what Opto compressors are good for:
- Transparent compression
- Smooth, musical compression
- Great on drums for transients coming through (due to attack)
- Great for vocals
- Good for a slow squeeze compression that recovers fairly quick
❌ What Are Opto Compressors Bad For?
Opto compressors do have drawbacks too. They have a lack of control, and aren’t great for transparency.
They’re not good at transient control, or aggressive sounding compression.
Here’s a list of what Opto compressors are bad for:
- Lack of control
- Bad for transients due to slow response
- Not transparent
PWM Compressors
PWM Compressor is short for Pulse Width Modulator. The unit uses a PWM to apply gain reduction to a sound source. This results in a completely transparent compression sound, that has no colour and extreme precise control.
With PWM compressors there are no artefacts introduced, thus has a clean sound.
You may not have heard of PWM compression until now, because they’re not very popular compression units. The reason for this may be due to the improvements in technology. We can now create completely transparent digital compression plugins, so there seems to be no point to emulate a PWM compression unit.
It’s more about the fact that PWM based gain control is basically a crude form of sampling very similar to digital (AD/DA based) gain control.
Fabien TDR – Gearspace.com
✅ What Are PWM Compressors Good For?
Here’s a list of what PWM compressors are good for:
- Transparent compression
- Extremely precise control
- No colour
❌ What Are PWM Compressors Bad For?
Here’s a list of what PWM compressors are bad for:
- Adding colour & aggression
Diode Bridge Compressors
Diode-Bridge compressors are hardware units that use diodes in a bridge formation to apply gain reduction. They turn AC signals to DC signals which compress the audio, and provide a thick, creamy, big sound.
Diode-Bridge compressors add the most colour out of all the analog hardware compressors, and they make anything that passes through them sound better.
You may not have seen many Diode-Bridge compressors because, using the diodes to apply compression adds a huge amount of distortion. Because of this they had to alter the design and drop the gain by a large amount.
This added some background hum and noise to the Diode-Bridge, and made them less popular.
However, due to improvements in technology, you’re now seeing more Diode-Bridge compressors being made, and without the noise.
There are some great plugin emulations of diode compressors, including the Arturia DIODE-609, the Lindell 254E, and more.
✅ What Are Diode Compressors Good For?
Here’s a list of what Diode compressors are good for:
- Thick, creamy compression
- Master glue
- Instrument group glue
- Incredible control
❌ What Are Diode Compressors Bad For?
Here’s a list of what Diode compressors are bad for:
- Transparent compression
- Transient control
Digital Compressors
Digital compressors are computer software that use code to either model analog circuitry of old compressors, or use code to provide clean gain reduction to your audio. They often have a precise clean sound.
They have the most control out of all the compressor types with attack, release, threshold, ratio, knee, lookahead, sidechain & more.
Digital compressors can either model old analog hardware, using specific technologies such as P-Spice to model circuity, or they can provide clean, transparent compression with extreme precision.
Popular fully digital compressors include:
- FabFilter Pro C2
- Sonible smart:comp
- Melda Production MComp
Digital compression plugins are extremly versatile, and can be used to control transients, smooth out vocal takes, and provide transparent gain reduction for anything you want. They don’t have any particular colouration, drive or warmth.
✅ What Are Digital Compressors Good For?
Here’s a list of what Digital compressors are good for:
- Clean, precise compression
- Transient control
- Thickness without colouration
- Transparent compression
- Amount of control
❌ What Are Digital Compressors Bad For?
Here’s a list of what Digital compressors are bad for:
- Colouration, warmth, drive
- Harmonically rich compression
- Vibe
Multi-band Compressors
A Multiband compressor is a tool that applies gain reduction to certain frequency ranges of an audio spectrum. You can use it to individually compress the lows, mids and highs of a signal. They are great for mixing purposes.
Multiband compression is a digital compressor that is transparent, and doesn’t have any colouration or apply any warmth to your audio.
They are solely used for mixing purposes and are extremely useful in certain scenarios where you want different levels of gain reduction at different frequency ranges.
A great use of multiband compression is using it to independently sidechain the low end, or using multiband to a specific area of the reverb out of the way of the vocals to create a bigger space for them to sit in.
You can use multiband dynamics processors to control the gain reduction of a signal, and can also use them for frequency manipulation. Many multiband compressors will have options to apply upwards or downward compression, meaning you can accentuate certain frequencies or squash the dynamics.
✅ What Are Multiband Compressors Good For?
Here’s a list of what Multiband compressors are good for:
- Independent frequency range processing
- Transparent compression
- Smoothing out dynamic material that changes over time
- Creating big, punchy sounds
- Compression control
❌ What Are Multiband Compressors Bad For?
Here’s a list of what Multiband compressors are bad for:
- Ease of use
- Colouration, and warmth
Limiters
Limiters are extremely fast, transparent compressors, that are for are used to achieve loudness in tracks, and limit the db level they can exceed (using the threshold) all while introducing minimal artefacts.
They are often used in mastering to attain maximum loudness, without introducing distortion, or exceeding streaming service rules. Limiters can also be used to increase the loudness of individual tracks in a mix, but it’s rare.
One great use of limiting for mixing, is on vocals.
Vocals often need very short, snappy compression to catch the peaks of highly dynamic performances, and level them out, so that they sound consistent.
Often people use compressors on vocals, when really a limiter would work better for their scenario.
Limiters provide a quick compression, that will nip transients in the bud, and prevent dynamic performances from sounding too quiet or too loud at points. They also give a great increase in volume, and presence of vocals, sending them to front and centre almost immediately.
Compression and limiting used simultaneously on vocals is a fantastic chain for processing, for instance.
Great, transparent, clean limiters include: FabFilter Pro L, Waves L3 Ultramaximizer, & Waves L316. Another tool that’s phenomenal to use with limiting is Sonnox’s Oxford Inflator. This is useful for masters that need extra loudness, but limiting also introduce distortion. Oxford Inflator gets a few extra LUFS out of your master, without introducing those artefacts.
✅ What Are Limiters Good For?
Here’s a list of what Limiters are good for:
- Loudness without distortion
- Vocal processing
- Preventing redlining
- Short, snappy compression
❌ What Are Limiters Bad For? (Examples)
Here’s a list of what Limiters are bad for:
- Colourful, smooth compression
- Control
Expanders
Expanders are a dynamic processing tool that do the opposite of compression. They increase the dynamic range in your audio signal. There are two types of expansion: upwards & downwards expansion.
Expansion is a useful tool to use in mixing scenarios, and although they are different to compression, they apply a similar processing effect, and help to control the dynamics of your audio, so we wanted to include them.
They have the same control as compressors, using attack, release, ratio, knee, threshold etc. And, most expanders will usually have frequency range control, apart from transient shapers (which using expansion).
Upwards Expanders
Upwards expanders apply gain reduction by turning up anything above a certain threshold. This increases the dynamic range of your audio signal, and makes things louder.
Upwards expanders are used to emphasise the peaks of an audio signal. They can be useful for adding punch, grit, and loudness to things like drums, or heavy synth lines etc. An example of an upwards expander is Xfer’s OTT.
Upwards expansion makes everything sound really loud, and gives your audio a harsh tone if the dry/wet is on full. It’s best used in parallel or on a dry/wet of about 30%.
This gives your audio signal a nice lift, without destroying the sound.
Downwards Expanders
Downwards expanders apply gain reduction by turning down anything below the set threshold. They act similarly to a gate plugin, and prevent things like mic bleed.
The difference between a gate and an expander is that the gate will abruptly cut your audio off below a certain threshold.
Downwards expansion can do this when using a short attack, but generally applies a much smoother sound.
It’s good for lowering the background noise in recordings, reduce bleed, hum etc.
✅ What Are Expanders Good For?
Here’s a list of what Expanders are good for:
Upwards expansion:
- Adding punch to transients
- Adding grit, volume and drive
- Increasing the dynamic range
- Adding presence and clarity
- Transient processing
Downwards expansion:
- Noise reduction
- Removing bleed
- Smooth noise reduction
❌ What Are Expanders Bad For?
Here’s a list of what Expanders are bad for:
Upwards & Downwards:
- Clean, non-colourful dynamics processing
- Smooth processing
Summary
Compression is an extremely useful tool, and you need to understand it inside and out if you’re serious about working with audio. This article covered all the compression types, which you should use and where in your mixes.
We hope you enjoyed the article!
